Hot carrier degradation of mixed-mode polysilicon light emitting diodes

This paper investigates the degradation and reliability of polysilicon light emitters implemented in a standard 0.35 mu m CMOS process. A total of 48 identical hot carrier electroluminescent emitters were subjected to high temperature operating life tests. The results show the first reported degradation in reverse biased silicon light emitter intensity, consistent with hot carrier degradation. The degradation is shown to be strongly dependent on the stress current, while little to no dependence on temperature stress is noticed. With the device operating in a mixed-mode regime, it is postulated that hydrogen dissociation and generation of interface states through hot carrier stress increases the non-radiative tunnelling mechanisms reducing the optical intensity with increased stress. Degradation model parameters are extracted to predict light emitter lifetime and to provide long life design criteria for these polysilicon light emitters.